1. Field of the Invention
The present invention relates to a position registration method for a cellular mobile communications system which includes a plurality of base stations, a switching control station and a mobile station.
2. Description of the Related Art
In a cellular mobile communications system, a mobile station receives a forward link radio wave of a base station not only during calling but also during call waiting, discriminates an area in which the mobile station exists from the received signal and performs, if it enters a different service area, a position registration operation.
Increase of the number of mobile stations and reduction in size of areas increase the number of position registrations of call waiting mobile stations and suppress original pursuit call switching processing. Particularly where a large number of passengers having call waiting mobile stations board and move with a means of transportation such as an electric train or a bus, each time the means of transportation passes an area boundary and enters another service area, position registration operations are started at a time by the mobile stations, and in order to process a large number of position registration requests which are generated at a time in this manner, the load applied to the switch increases suddenly and original pursuit switching processing for calls in service is suppressed. Furthermore, the condition described above is liable to occur in rush-hours in the morning and in the evening, and in order to process such a large number of position registration requests as described above, a sufficient margin is required for the capacity of the equipment and this is economically disadvantageous.
A position registration system which reduces such a load to a switch caused by a large number of position registration requests as described above is disclosed in Japanese Patent Laid-Open No. 319168/1994 wherein a speed of movement of a mobile station is calculated to estimate a range of movement of the mobile station, and, when the mobile station goes out of the range, position registration is performed thereby to reduce the number of times of position registration. The position registration system, however, has the following problems.
The first problem resides in that the effect of reduction of the number of times of position registration is low. The reason is that the range of movement is an estimated value and the reduction effect is lost when the mobile station goes out of the estimated range.
The second problem resides in that the range within which the load reduction effect by the reduction of the number of times of position registration is enjoyed is narrow. The reason is that, where the mobile station moves over a long distance, it is difficult to accurately estimate the entire path of movement of the mobile station, and the reduction of the number of times of position registration based on an estimated route is effective only for limited areas.